By using the shorthand RenderingContext, methods and properties which can make use of any of these interfaces can be specified and written more easily; since <canvas> supports several rendering systems, it's helpful from a specification and browser implementation perspective to have a shorthand that means "one of these interfaces."

As such, RenderingContext is an implementation detail, and isn't something web developers directly use. There is no RenderingContext interface, and there are no objects which implement type RenderingContext.

The primary use of this type is the definition of the <canvas> element's HTMLCanvasElement.getContext() method, which returns a RenderingContext (meaning it returns any one of the rendering context types).